Family and population are closely linked. The size, age structure, and characteristics of a population are studied in demography. Factors like birth rates, death rates, and migration influence population size. In the UK, the population grew from 10.5 million in 1801 to 61 million in 2007 due to declining death rates and increasing births, though birth rates have since declined. An aging population with fewer births and more deaths means the UK population is projected to rise more slowly to 71 million by 2031.